The cams with which the present invention is principally concerned have long been well known in configuration, per se, and have become identified generically by the term "gerotor". They are characterized by internal or external contours which, unlike the teeth of conventional gears, are lobed and exhibit continuous curvature rather than discontinuous or irregular shapings. When such contouring is exactly in accordance with theory, mated inner and outer cams, or one such cam cooperating with a circular array of rollers in place of the other, lend themselves to highly-efficient cooperations wherein all lobes and/or rollers are constantly in working meshed contact while one is orbited within the other. For the latter purpose, the outer one of the two cams, or cam and array of rollers, normally has a number of lobes or rollers which exceeds by one the number of the other. Examples of constructions in which such units are advantageously used in such devices as pumps, hydraulic motors and speed changing transmissions may be found in U.S. Pat. No. 3,574,489 -- Pierrat and in copending application Ser. No. 530,224, filed Dec. 6, 1974, for "Mechanical Drives" -- Pierrat. Contouring of the cams is so critical, and has been so difficult to achieve with the requisite precision, that early versions were matched as sets which were worn to about the right shapings by running-in which burnished their surfaces to an acceptable operating fit. Subsequent versions, precise enough to allow for interchangeability, have since become commercially available, but are evidently difficult to produce because their cost is very high. The manufacturing technique which suggests itself is that of guiding a circular milling cutter of the like around the periphery which is to be shaped into the lobes, under the direction of a contour guide or in accordance with a computed program to which either or both of the cutter and cam blank are slaved as to relative motion. However, the sizes and lobe numbers of such cams may vary widely, and the contouring guides or programs must be of equal variety and based upon complex calculations and/or empirically-derived data. Special-purpose cutting machinery capable of performing such needed contouring tend to be expensive and to call for uncommon operating skills.
Our improved and unusual approach to realizing the critically-contoured lobed cams, with great precision and ease and economy, requires neither contour guides nor programmed computer-controlled automatic cutting machines; instead, it uniquely recognizes and takes into account a distinctive combination of synchronized reverse-direction rotary and orbital motions and develops these by way of a novel and uncomplicated fixture in which the needed special relative motions between a cutter and cam blank are automatically and accurately generated and are readily changeable to meet varied contouring specifications.